Process of treating slag for the production of red pigments



UNITED STATES PATENT OFFICE.

JAMES P. PERKINS, OF YONKERS, NEIV YORK.

PROCESS OF TREATING SLAG FOR THE PRODUCTION OF RED PIGMENTS.

SPECIFICATION forming part of Letters Patent No. 429,056, dated May 27, 1890. Application filed May 13, 1889- Renewed March 6,1890. Serial No. 342,916. (No specimens.)

To all whom it may concern:

Be it known that I, J AMES PLINY PERKINS, a citizen of the United States, residing at Yonkers, in the county of VVestchester and State of New York, have invented certain new and useful Improvements in Processes of Treating Slag for the Production of Red Pigments;

and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

My invention consists in the process, hereinafter to be described and claimed, of treating silicious ferrnginous slags for the production of red pigments.

By the application of my process a variety of bright-red pigments of a most pronounced color are produced. These colors belong to the class commonly known as Venetian reds. The silicious ferruginous slag which I employ as the raw material in my process is most commonly found as a by-product in the manufacture and working of wrought-iron, though it may be produced in other ways in a form suitable for the application of my process. The best quality of this slag is produced in puddling and reheating furnaces. It is nearly black in color, of great specific gravity, and consists of a nearly-pure silicate of iron mixed with ferrous oxide. This slag, as above described, I pulverize in any suitable pulverizing apparatus to a degree of fineness known in the art as one hundred and ninety mesh, or more. It is not necessary that it should be pulverized to a degree finer than that, and my process may be carried out with a fair degree of success with slag ground to a lesser degree of fineness than that mentioned.

Thesecond step of my process consists in subjecting the slag, pulverized as above described, to the action of heat with access of air. This calcining in a suitable furnace changes the color of the pulverized slag from a black. or slate color to a dark reddish brown or seal brown, all as described in my previous patent, issued May 24, 1887, and numbered 363,67 3.

The third step in my process consists in treating the slag which has been pulverized and calcined, as above described, with sulphuric acid. The acid may be mixed with the pulverized and calcined slag in the ordinary way by stirring with spades or paddles or in any suitable mechanical mixing-machine. The amount of sulphuric acid to be mixed with a given quantity of pulverized and calcined slag varies according to the quality of the slag and the particular shade of color which it is desired the resulting pigment shall present. The amount of acid, however, is always much less than that required in the process described in my application filed April 19, 1889, Serial No. 307,869, in which the method described and claimed contemplates the treatment of the pulverized slag with sul-v phuric acid without the intermediate step of heating or calcining as employed in the method which is the subject of this application. The acid may be used undiluted, in its commercial form of oil of vitriol, or it may be diluted with water, and I prefer this method of applying it, as its action is slower, more moderate, and more uniformly diffused through the mass of pulverized slag. \Vhen undiluted, the action of the acid is intense, local, and uneven. It attacks too violently those particles with which it first comes in contact, and being absorbed by these does not get to other particles. Another method of obtaining the same eifect as that resulting fromthe dilution of the acid is to dampen or moisten the pulverized slag with the given quantity of water before applying the undiluted acid. The result is obviously the same, though the preferable method is to dilute the acid first and then apply the dilute solution to the drypulverized slag. The perceptible effects of this the third step in my process are the liberation of heat and the caking or solidification of the mass of slag. NVhat was formerly a fine powder be- I comes a solid mass, though brittle and easily broken up. The color of the mass changes from the dark shade which the slag has after pulverization and calcination to a gray or whitish tinge. If water is used to dilute the acid, as above described, a considerable quantity of steam is given off during this step of my process, and if the acid is used in undiluted form a certain amount of steam is still given off during this step of the process.

The fourth step in my process consists in heating the substance produced by the steps hereinhefore described to a red heat in any suitable furnace. The caked mass remaining after the completion of the third step in the process should be broken up, so as to be eapableof convenienthandlingand introduction into the furnaccQ The furnace should be so constructed as to permit the escape of the fumes given off on heating the charge and to allow access of air when desired. The result of this process of treating slags of the nature described in the manner above set out is a bright-red pigment of the most desirable of those shades known as Venetian reds. The pigment is of a soft nature and can easilybe ground to an impalpable smooth powder. It mixes and blends easily with other pigments and grinds perfectly with oil. The ground pigment is f rec from grit and of unusual smoothness.

The above is a full description of my proeess of treating silicious ferruginous slag in order to produce red pigments, and my invention, as it has been hereinbefore described and as it will be hereinafter claimed, is independent of the question of the chemical composition of the pigment which is produced as a result of the application of my process, and is equally independent of the question of what chemical reactions occur in the various steps of the process. Chemical analyses of the resulting product of my process of treating slag tend to show, however, that it consists of an intimate mixture of ferric oxide and separated or precipitated silica, and it is believed that the reactions which take place during the process are the following:

The heating or calcining of the pulverized slag in the second step of this process oxidizes the ferrous. oxide which exists in the slag uncombined with ferrous silicate, and forms red ferric oxide. This oxidizing action is not suiliciently powerful to overcome the affinity existing between the particles of iron and silica composing the ferrous silicate, and the latter remains unchanged and imparts its dark color to the product resulting from the second step of the process. The sulphuric acid in the third step of the process attacks the ferrous silicate, which has remained unchanged during the second step, forming ferrous sulphate and silica. The action of the heat in the fourth step of the process decomposes the fcrrous sulphate, leaving behind ferric oxide as a bright red powder. Any further residue of the ferrous oxide of the slag which may not have been further oxidized during the second step of the process or attacked by the sulphuric acid in the third step and which has remained unchanged, intermixed with the ferrous sulphate, is at the same time set free by the decomposition of the sulphate by heat and is also oxidized to ferric oxide, probably by the combined action of the sulphuric acid and sulphuric trioxide set free on heating the forrous sulphate. During the application of heat in the fourth step of the process sulphuric dioxide gas passes oil in fumes.

As before stated, the shade of color in the pigment produced by this process may be varied by varying the amount of sulphuric acid used, the bright reds being produced when the larger quantities of acid are used and the darker ones when a less quantity of acid is used, and it is believed that this is due to the fact that when the lesser quantity of acid is used the reactions are not sutliciently general and powerful to attack all the ferrous silicate, and a certain quantity exists, therefore, unchanged in the resulting pigment, imparting its dark color thereto.

The process hereinbefore described is an improvement on the process for producing the same or nearly similar pigment described and claimed in my application filed April 19, 1889, Serial No. 307,869, in that a considerable saving is made in the amount of sulphuric acid used. In localities where sulphuric acid costs heavily and fuel is comparativel y cheap the process herein described would be preferable to that covered in the application above referred to.

The pigments produced by my process are brighter and more pronounced in color and they are more homogenous in composition than any that can be made by the mixture of the ordinary Venetian reds with the ground silica, and it is believed that this is due to the fact that my process produces a mixture of ferric oxide with silica in the separated or precipitated and extremely fine condition which it assumes when it is set free from certain silicates decomposable by acids and then heated. In the separated or precipitated condition silica is finer and more pulverulent than it can be when produced by the most complete grinding of quartz-rock or quartzose mineral, for the particles thus obtained by grinding will consist of particles of large crystals. In the separated or precipitated condition, also, silica is opaque, while the minute particles of crystals or crystalline rock obtained by grinding would be transparent or translucent. Consequently it is believed that this is the reason why the pigments produced by my process are so much more pronounced in color than the weaker lighter shades produced by mixing ordinary Venetian reds with ground silica. Separated or precipitated silica has, furthermore, a much greater power to hold or bind colors than crystalline silica.

Separated or precipitated silica is apparently neutral so far as concerns the dimming or affecting the color of the ferric oxide with which it is mixed in the proportions resulting from the operation of my process. \Vhile not prepared to give a positive reason for this result, I am inclined to believe that it is due to the fact that the separated or precipitated silica is in so finely comminuted a condition that it to a large degree occupies the interstices between the particles of ferric oxide IIO without separating the latter, and thereby second, heating it with access of air; third, diffusing the coloring-matter, as do the larger treating with sulphuric acid, and, fourth, apparticles of crystalline silica produced by the plying heat to the mass, all substantially as ordinary process of grinding. described.

5 Having" therefore described my invention, In testimony whereof I afiix my signature [5 whatI claim as new, and desire to protect by in presence of two witnesses.

Letters Patent, is JAMES P. PERKINS.

The process of treating silicious ferrugi- WVitnesses: nous slags for the production of pigments, A. P. SMITH, 10 which consists in, first, pulverizing the slag; WM. H. CLARKSON. 

